Semiconductor wafers can be transferred from one tool to another while being exposed to ambient temperature and ambient pressure levels. A tool can process or inspect the semiconductor wafer within a chamber that can maintain temperature and pressure levels that differ from the ambient temperature and ambient pressure level.
The semiconductor wafer is usually positioned on a chuck when it is processed or inspected. The temperature of the chuck is higher than the ambient temperature and when the semiconductor wafer is placed on the chuck it experiences a thermal expansion.
This thermal expansion increases the uncertainty level associated with any processing or inspection process, and may reduce the speed and accuracy of such inspection or processes. During inspection a larger area of the semiconductor wafer can be scanned in order to account for the thermal expansion.
Furthermore, when an inspection tool is required to provide class images with the defect centered within 10% of the image size, the thermal expansion between defect detection and the class image grab increases the uncertainty of defect center.
A thermal expansion that exists during image grab may also cause miss-registration of frames which is equivalent to enlarging the spot. This effect depends on the expansion slope and is more severe at the wafer edge, shortly after the semiconductor wafer has been loaded.